Choloesteric liquid crystal display

ABSTRACT

A cholesteric liquid crystal display is provided, including a substrate, a first electrode layer disposed on the substrate, and a liquid crystal layer disposed on the first electrode layer, wherein the liquid crystal layer comprises at least two liquid crystals having different sensitivities to driving frequencies, mixed with each other, and the liquid crystals having a greater initial state-transition temperature are more sensitive to driving frequency.

This application is a Divisional application of pending U.S. patent application Ser. No. 13/191,432, filed Jul. 26, 2011 and entitled “CHOLESTERIC LIQUID CRYSTAL DISPLAY AND FABRICATION THEREOF”, which claims priority of Taiwan Patent Application No. 099145762, filed on Dec. 24, 2010, the entirety of which is incorporated by reference herein.

BACKGROUND

1. Technical Field

The disclosure relates to a display device, and relates to a cholesteric liquid crystal display and fabrication thereof.

2. Description of the Related Art

For the current energy-saving trend, light, thin and electricity saving displays are main stream in the display field. For example, bistable liquid crystal displays, such as cholesteric liquid crystal displays have many features, such as high brightness, high contrast, saving energy, memorable characteristic, wide viewing angles and no flicker. The bright state (planar texture/state) and dark state (focal conic texture/state) of a cholesteric liquid crystal display are maintained when an electric field is removed. Therefore, cholesteric liquid crystal displays are an important developing technology.

Cholesteric liquid crystals can reflect a specific wavelength at a planar texture/state. When the reflected wavelength is in a visible-light region, human eyes can receive the reflected light. The currently developed cholesteric liquid crystal displays are single colored and a new cholesteric liquid crystal display which can present multi-colors and can reflect light with multiple-reflecting wavelengths is required.

U.S. Pat. No. 4,031,529 uses a heat driving method and electric fields with various frequencies for liquid crystals to have different dielectric constants, such that liquid crystals having different optical states are obtained. U.S. Pat. No. 5,223,937 discloses an ink jet recording apparatus which can provide high quality pictures using a static method when receiving various image signal frequencies. In the patent, the driving voltage and temperature are different according to different signal frequencies.

SUMMARY

An embodiment of the disclosure provides a cholesteric liquid crystal display, comprising a substrate, a first electrode layer disposed on the substrate, and a liquid crystal layer disposed on the first electrode layer, wherein the liquid crystal layer comprises at least two liquid crystals having different sensitivities to driving frequencies, mixed with each other, and liquid crystals having a greater initial state-transition temperature is more sensitive to driving frequency.

An embodiment of the disclosure further provides a method for displaying a cholesteric liquid crystal display. A cholesteric liquid crystal display, comprises a substrate, a first electrode layer disposed on the substrate, and a liquid crystal layer disposed on the first electrode layer, wherein the liquid crystal layer comprises at least two liquid crystals having different sensitivities to driving frequencies mixed with each other, and the liquid crystals having a greater state-transition temperature are more sensitive to driving frequency. Heat and electricity comprising voltage or driving frequency are applied to drive the liquid crystals for brightening or darkening thereof, wherein the applied voltage or driving frequency are changed with regard to different liquid crystals for liquid crystals to have different changing amounts of state-transition temperatures,

BRIEF DESCRIPTION OF DRAWINGS

The disclosure can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein,

FIG. 1 is a cross section of a cholesteric liquid crystal display of an embodiment of the disclosure.

FIG. 2 is the characteristics of liquid crystals in the liquid crystal layer with reflectivity as a function of temperature.

DETAILED DESCRIPTION

It is understood that embodiments are provided as examples to teach the broader inventive concept, and one of ordinary skill in the art can easily apply the teaching of the present disclosure to other methods or apparatuses. The following discussion is only used to illustrate the disclosure, not limit the disclosure.

FIG. 1 is a cross section of a cholesteric liquid crystal display of an embodiment of the disclosure. Referring to FIG. 1, a substrate 102 is provided. In an embodiment, the substrate 102 is a transparent substrate, such as glass or polyethylene terephthalate (PET). A first electrode layer 104 is formed on the substrate 102. In an embodiment, the first electrode layer 104 is a transparent conductive layer, such as indium tin oxide (ITO) or indium zinc oxide (IZO). A liquid crystal layer 106 is formed on the first electrode layer 104. In an embodiment, the liquid crystal layer 106 comprises at least two liquid crystals having different sensitivities to driving frequencies, mixed with each other, wherein liquid crystals having a greater initial state-transition temperature are more sensitive to driving frequency. In other words, the liquid crystals having a greater initial state-transition temperature are more sensitive to driving frequency than the liquid crystals having a lower initial state-transition temperature. A light absorbing layer 108 is formed on the liquid crystal layer 106. In an embodiment, the light absorbing layer 108 is black. The light absorbing range of the light absorbing layer 108 is dependant upon production design concern to absorb visible light, ultraviolet light or infrared light. A second electrode layer 110 is disposed on the light absorbing layer 108, wherein the second electrode layer 110 may be a transparent electrode or an opaque electrode, wherein the second electrode layer 110 may be disposed over or under the light absorbing layer 108. In an embodiment, the second electrode layer 110 is formed of metal having high reflectivity, such as silver. The disclosure does not limit the light absorbing layer 108 to be over the liquid crystal layer 106. The light absorbing layer 108 can be disposed between the liquid crystal layer 106 and substrate 102.

The characteristics of liquid crystals in the liquid crystal layer are illustrated in accordance with FIG. 2, wherein FIG. 2 shows a diagram with reflectivity as a function of temperature. The diagram includes a temperature-reflectivity curve of a first liquid crystal, a temperature-reflectivity curve of the first liquid crystal applied with high frequency voltage, a temperature-reflectivity curve of a second liquid crystal, and a temperature-reflectivity curve of the second liquid crystal applied with high frequency voltage. The first liquid crystal reflects a light with a first wavelength and second liquid crystal reflects a light with a second wavelength. As shown in FIG. 2, the first liquid crystal requires greater state-transition temperature than the second liquid crystal, and the first liquid crystal is more sensitive to high frequency voltage than the second liquid crystal. As shown in FIG. 2, the first liquid crystal applied with a high frequency voltage, such as the condition of 10V and 10 KHz, requires lower state-transition temperature than the second liquid crystal applied with the high frequency voltage. The disclosure simultaneously applies high frequency voltages to the first liquid crystal and second liquid crystal having different state-transition temperatures to control reflectivity of a specific wavelength of the first and second liquid crystals in the liquid crystal layer according to sensitivity differences of the first and second liquid crystals to driving frequency for the cholesteric liquid crystal display to present reflection of light with different wavelengths. Result of driving the liquid crystal may change when applied voltage or driving frequency varies.

EXAMPLE

The first liquid crystal having a blue color is more sensitive to driving frequency than the second liquid crystal having a red color. The description of the liquid crystal being sensitive to driving frequency is identical to the amount of change of the state-transition temperature of the liquid crystal when applied with a high frequency. The liquid crystal is more sensitive to driving frequency means that the state-transition temperature of the liquid crystal has a greater change when applied with a driving frequency.

The blue liquid crystal has a state-transition temperature of 75° C., and the red liquid crystal has a state-transition temperature of 65 C. When both the blue liquid crystal and red liquid crystal are applied with a high frequency voltage, such as the condition of 10 KHz and 10V, the state-transition temperature of the blue liquid crystal is reduced to 55° C. and state-transition temperature of the red liquid crystal is reduced to 60 C.

An embodiment of the disclosure provides a displaying method of a multi-color cholesteric liquid crystal display according to the characteristics of the liquid crystals described above.

First table Optical state Driving condition Blue Red All color 100 V ◯ ◯ brightening All color 80° C. X X darkening Red color 70° C. ◯ X darkening Blue color 10 V, 10 KHz, 55° C. X ◯ darkening ◯: Bright state; X: Dark state

Referring to the first table, the example can apply a voltage of 100V to switch a blue liquid crystal and red liquid crystal to a bright state. Therefore, the blue and red liquid crystals are presented as planar textures and the cholesteric liquid crystal display presents a color mixture of blue and red. The example can apply a temperature of 80° C. (the temperature higher than the state-transition temperature of the blue and red liquid crystals) to switch the blue and red liquid crystals to a dark state. The blue and red liquid crystals are presented as focal conic textures and the cholesteric liquid crystal display presents the color of the light absorbing layer (for example a dark color). The example can apply a temperature of 70° C. (the temperature higher than the state-transition temperature of the red liquid crystal but lower than the state-transition temperature of the blue liquid crystal) to darken the red liquid crystal. The cholesteric liquid crystal display presents the color of the blue liquid crystal. The example can apply a temperature of 55° C. and a high frequency voltage (for example the condition of 10 KHz and 10V). Since the state-transition temperature of the blue liquid crystal is reduced to be lower than the state-transition temperature of the red liquid crystal after applying the high frequency voltage, the temperature 55° C. can darken the blue liquid crystal but the red liquid crystal remains at a bright state. The cholesteric liquid crystal display presents the color of the red liquid crystal.

According to the description above, the example can control two reflecting wavelengths of light in a liquid crystal layer by adjusting the application of temperature and voltage frequency. Although the disclosure above only discloses a cholesteric liquid crystal display with two kinds of liquid crystals and displaying methods thereof. The disclosure is not limited thereto. The disclosure can further add a third liquid crystal having a greater initial state-transition temperature than the first liquid crystal and more sensitive to driving frequency than the first liquid crystals. Accordingly a high voltage is simultaneously applied to the first, second and third liquid crystals having different state-transition temperatures to control reflectivity of a specific wavelength of the first, second and third liquid crystals in the liquid crystal layer according to sensitivity differences of the first, second and third liquid crystals to driving frequency for the cholesteric liquid crystal display to present reflection of light with different wavelengths.

While the disclosure has been described by way of example and in terms of the preferred embodiments, it is to be understood that the disclosure is not limited to the disclosed embodiments. It is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements. 

What is claimed is:
 1. A cholesteric liquid crystal display, comprising: a substrate; a first electrode layer disposed on the substrate; and a liquid crystal layer disposed on the first electrode layer, wherein the liquid crystal layer comprises at least two liquid crystals having different sensitivities to driving frequencies, mixed with each other, and the liquid crystals having a greater initial state-transition temperature are more sensitive to driving frequency.
 2. The cholesteric liquid crystal display as claimed in claim 1, further comprising a light absorbing layer.
 3. The cholesteric liquid crystal display as claimed in claim 2, wherein the light absorbing layer absorbs visible light, ultraviolet light or infrared light.
 4. The cholesteric liquid crystal display as claimed in claim 2, further comprising a second electrode layer, wherein the second electrode layer is a transparent electrode or opaque electrode.
 5. The cholesteric liquid crystal display as claimed in claim 4, wherein the second electrode layer is disposed over or under the light absorbing layer.
 6. The cholesteric liquid crystal display as claimed in claim 1, wherein the liquid crystal layer comprises a first liquid crystal and a second liquid crystal, and the first liquid crystal requires greater state-transition temperature than the second liquid crystal, and first liquid crystal is more sensitive to driving frequency voltage than the second liquid crystal.
 7. The cholesteric liquid crystal display as claimed in claim 6, wherein the first liquid crystal reflects a light with a first wavelength and the second liquid crystal reflects a light with a second wavelength.
 8. The cholesteric liquid crystal display as claimed in claim 6, wherein the liquid crystal layer further comprises a third liquid crystal, the third liquid crystal requires greater initial state-transition temperature than the first liquid crystals, and the third liquid crystal is more sensitive to driving frequency than the first liquid crystal. 